1. Field of the Invention
The invention relates generally to control systems for load pulling vehicles and more particularly to a control system for an automatic gear shift mechanism of a traction vehicle.
2. Related Art
In addition to the ordinary requirements of safe driving and mechanical vehicle operation, drivers of traction vehicles, such as tractor trailer combinations, were constantly faced with changing circumstances affecting vehicle handling, operation and response, all related to the type and nature of a trailing vehicle load. Trailing vehicle loads caused changes in the traction vehicle handling and operating characteristics including engine performance, and transmission performance. Such loads, for example, required the traction vehicle driver to employ longer duration engagement of lower gear ratios as a function of the load characteristics.
The pulling of loads by traction vehicles resulted in increased engine wear engine load and increased rate of clutch wear when starting and during speed change gear shifts.
Further, the size and configuration of a trailing vehicle load mandated special steering considerations such as wider turn radii. The vehicle operator was required to always be cognizant of whether a trailing vehicle load was connected, the size of the load, the load configuration and other factors all of which were subject to change.
Such factors greatly affected the manner in which the traction vehicle was to be operated by the operator and placed increase demands on drivers who were often subject to extended working hours, especially long haul tractor trailer drivers.
Increased demands were also placed upon tracked vehicle operators when a vehicle was pulling a load. For example, a tank operator pulling a trailing vehicle was required to be concerned about not only battle conditions but, in addition, due to limited visibility and the like, had to be concerned with terrain variations and persons in the vicinity of the traction and trailing vehicles and the greatly altered driving characteristics of the traction vehicle.
German patent document DE-OS No. 29 52 204 illustrated an attempt to provide a controller for a gear shift mechanism to control gear shifts into higher or lower gear as a function of a trailing vehicle load. Such controller was apparently designed for the purpose of reducing fuel consumption and was not capable of assuring that the traction vehicle operating characteristics would be similar whether or not it was pulling a load.
In German patent document DE-OS No. 33 14 800, a gear shift mechanism controller was disclosed. The controller operated as a function of instantaneous engine driving torque and vehicle acceleration. The controller was incapable, however, of detecting whether a trailing vehicle was being pulled by the traction vehicle and altering shift patterns as a result. In the magazine Automobil-Industrie, No. 6/86 pp. 743-748, an electropneumatic gear shift for a multi-speed mechanical utility vehicle transmission was disclosed to include visual indicators for displaying both vehicle speed and the shifted gear which was in engagement.
Attention is also directed to German patent document DE-OS No. 36 10 461 which disclosed a device for steering both the front and rear wheels of a motor vehicle. The device included means for detecting a vehicle load on the rear wheel axle and as a function of such load, changing the ratio of the steering angle of the rear wheels relative to the steering angle of the front wheels.